This invention relates generally to an ejection system and method for emergency crewmember aircraft separation. The ejection system takes into account such parameters as crewmember-seat mass, flight dynamics at the time of ejection, and ambient conditions, to insure a safe ejection for the individual crewmember.
Since the introduction of ejection seats in operational aircraft, there have been performance limitations on the equipment. An area of principal concern is the initial phase of emergency egress from the cockpit. Early attempts considered compression springs, compressed air, or an explosive charge. These efforts recognized the effects of rate of onset acceleration which is commonly referred to as "jolt". The use of an explosive charge was selected for ejection since such systems provided some control regarding peak G's and rate of onset.
Although performance has been improved and the hardware refined in recent years, an explosive charge remains the principal means of egress from the cockpit. With the improved performance and maneuverability of modern high speed aircraft, explosive charge ejection systems may exceed human tolerances depending upon the environmental and flight conditions existing at the time of ejection.
From the standpoint of human tolerance to vertical acceleration, an important factor in rocket design is the control of the rate of burning of the powder in the charge. This determines the rate of build-up of tube pressure which, in turn, determines the rate of onset acceleration. Further, the peak pressure generated in the tube by the burning of the powder produces the peak G. A peak of 20 G's at a rate of onset of 250 G's per second for a duration not to exceed 0.1 second is considered within the safe region of human tolerance. However, traditional systems cannot compensate for changing environmental conditions. For example, the surrounding G field is additive to peak G's. A catapult that applies 18 G's of acceleration to a crewmember at ground conditions will essentially apply 23 G's to the crewmember's spine when the aircraft is under a 5 G environment at the time of ejection. Another changing condition involves the need to consider the variation of ejected mass due to the increasingly diverse pilot population. Initial design catapult requirements consider only the nominal crewmember weight. Very heavy or light crewmembers will produce different peak G's and rates of onset.
Several patents involve sophisticated systems, designed to improve ejection safety. U.S. Pat. No. 2,996,272 discloses an apparatus for ejecting crewmembers from high speed aircraft. A constant thrust type rocket using solid fuel controls ejection thrust. Thrust is automatically varied by thrust vanes carried by the rocket and located at the rocket nozzle.
U.S. Pat. No. 3,027,125 discloses a piston type propelling system in which many charges spaced along the outer tube of the piston are successively unported as the piston moves down the tube. A gun type catapult provides thrust until the ejection seat leaves the cockpit. The rocket motor then fires and provides additional upward velocity.
The performance curves of current catapult systems involve a spike peak pressure and peak G, with the parameters decaying until tube separation. Depending upon the ejected weight this fluctuation can result in a loss of 20 to 25 feet of altitude, which in a low level ejection can be critical. With a rocket catapult the only way to compensate for this loss is to increase the initial ejection force. However, this results in increased pressure, peak G's, and rate-of-onset that will place the small crewmember in a position of exceeding tolerance limits for spinal loading.
The novel features which are believed to be characteristic of the invention, both as to the catapult ejection system and method, together with further objects and advantages thereof, will be better understood from the following description in connection with the accompanying drawing in which presently preferred embodiments of the invention are illustrated by way of examples. It is to be expressly understood, however, that the drawing is for purposes of illustration and description only, and is not intended as a definition of the limits of the invention.